Methods for scanning an object to be examined with a CT system are generally known and utilize, for example, circular scans, sequential circular scans with forward movement or spiral scans. Other types of scans which are not based on circular movements are also possible, for example scans with linear segments. Absorption data from the examined object are recorded from different recoding angles using at least one X-ray source and at least one opposite-arranged detector, and the absorption data or projections collected in this way are then used for computing sectional images through the examined object with the aid of corresponding reconstruction methods.
Methods for the image reconstruction are generally used for the reconstruction of computer-tomography images from X-ray CT data sets recorded by a computer tomography device (CT device), meaning data from the recorded projections, wherein these methods are based on a back projection of the filtered measuring data. One of the standard methods used nowadays is the so-called filtered back projection technique (FBP), for which data are detected and are then transformed to the frequency range. A filtering occurs in the frequency range and the filtered data are subsequently transformed back. With the aid of the filtered data, a back projection is then realized to the individual voxels within the volume of interest.
One problem with the image reconstruction method based on the back projection of filtered measuring data is that when using the fan-beam or the cone-beam geometry for the measuring operations, a back projection weight is used which depends on the location of the image point or pixel that is to be computed. This local variance in the back projection weight leads to undesirable image characteristics because the image noise and the local resolution are not distributed uniformly, but non-homogeneously throughout the image.
One remedy for this problem is to use a rebinning, for which a so-called “rebinning” step is carried out following the data detection. In this step, the data generated by the beam that is spreading in the manner of a fan once it leaves the source, are rearranged so as to resemble X-ray beams with parallel rays impinging on the detector.
It is the object of the present invention to provide a reconstruction method for CT images, which delivers high image quality even if a rebinning step is omitted. The object is furthermore to provide a corresponding computer and control unit, a CT system, a computer program and a computer program product.